This invention relates generally to force output devices, and more particularly to flat-coil actuators for use in force feedback interface devices.
Actuators are used in a variety of devices to output a desired magnitude and direction of force. Haptic (xe2x80x9cforce feedbackxe2x80x9d) interface devices are used to interface a human with a host computer and use actuators to output feel sensations to the user to enhance or embellish the user""s interaction with an application program running on the host computer. Examples of mass-market force feedback interface devices include joysticks and mice. A force feedback joystick allows the user to input direction information to a computer by moving the joystick handle in provided degrees of freedom, and uses actuators to output forces in those degrees of freedom to enhance events and interactions occurring in an application program such as a computer game. A force feedback mouse can similarly output forces in the degrees of motion of the mouse to assist the user in moving a cursor to icons or windows in a graphical user interface, for example.
Flat-coil actuators are a particular type of actuator which consist of an electric coil (one or more adjacent loops of wire) which is placed in a small air-gap between pairs of opposing-pole permanent magnets such that when electric current is passed through the coil, a force is generated, thereby applying force to and causing motion in an attached linkage. The structure of a typical rotary flat-coil actuator is shown in FIG. 1a, which is a top plan view, and FIG. 1b, which is a side sectional view. Actuator linkage (rotor) 1 rotates about an axis of rotation 4 to provide motion and a rotary force output at one end 6 of the linkage 1. In a force feedback interface device, the end 6, for example, can be coupled to another linkage in a mechanism or directly to a manipulandum that is grasped by a user, such as a mouse, joystick handle, stylus, trackball, etc. The flat coil 2 is provided at the other end of the linkage 1. Stator magnets 3 surround the coil 2, where two magnets are positioned above the coil 2 and two magnets are positioned below the coil 2. Magnet backing irons 5 are coupled to the magnets, where one iron is positioned above the coil and one iron is positioned below the coil.
In comparison with many other types of electric actuators, flat-coil actuators are relatively low friction, low backlash (direct drive), low motion range, low force output, and high-speed. Flat-coil actuators are typically used in applications requiring high-precision, small motions. The most common use of flat-coil actuators is in computer hard disk drives: a rotary flat-coil actuator controls the position of the magnetic heads moving across the surface of the spinning disk drive platter(s). In haptic or force feedback mechanisms, flat-coil actuators can be used to drive one or more links in a variety of types of mechanisms and interface applications.
Current rotary flat-coil designs for haptic mechanisms based on pre-existing disk-drive flat-coil actuators, such as described in U.S. Pat. No. 5,642,469, have some significant limitations. One limitation is that the large footprint of the actuator precludes the use of multiple flat-coil actuators in close proximity. Multiple adjacent flat-coil actuators would allow more compact haptic mechanisms to be used. Another limitation is that position sensing in disk-drive flat-coil actuators is often performed using a dedicated read-only disk surface which contains factory-written positioning data to be read by the magnetic head for that surface. This approach is unfeasible for haptic mechanisms since no spinning disk surface is available. Some disk drive implementations have an alternate position sensing technique using an external optical encoder which is connected to the flat-coil actuator by either an extension of the linkage or by some sort of belt drive mechanism. However, this approach again increases the size of the flat-coil actuator footprint, which is an undesirable characteristic. Yet another limitation is that flat-coil actuators are inherently limited in performance by the amount of power they can dissipate as heat before the device fails (insulation burns or wire melts). Improvements in the heat dissipation characteristics of a flat-coil actuator would increase actuator performance.
The present invention describes a flat-coil actuator embedded in a linkage of a force feedback device, and which also includes an embedded sensor. This configuration allows more compact force feedback devices to be implemented.
More particularly, a flat-coil actuator of the present invention comprises a linkage operative to rotate about an axis. The linkage has two connection points, where one of the connection points is coupled to a ground. A flat coil is embedded in the linkage between the connection points. A plurality of magnets are positioned approximately parallel to the flat coil and grounded with respect to the linkage, where a force is produced on the linkage when a current is flowed in the flat coil. An embedded position sensor can be coupled to the linkage; for example, the sensor can include at least a portion of a code disk coupled to the linkage at the axis and an emitter/detector for detecting motion of the portion of said code disk. The linkage preferably surrounds the entire coil in a plane perpendicular to the axis. Furthermore, the flat coil preferably surrounds a non-conductive core that adds mechanical strength to the linkage.
A force feedback device incorporating the flat-coil actuator of the present invention includes a flat-coil actuator as described above, where a force is produced on the linkage when a current is flowed in the flat coil. A sensor such as an optical encoder is coupled to the linkage for detecting motion of the linkage about the axis. A user manipulandum graspable by a user is coupled to a connection point of the linkage such that the force is transmitted to the manipulandum. One of the connection points of the linkage is coupled to a ground, and the other of the connection points is coupled to the user manipulandum. In one embodiment, an intermediate linkage is coupled between the linkage and the user manipulandum. A five-bar linkage embodiment provides two flat-coil actuators and two intermediate linkages rotatably coupled to each other.
A method of the present invention for using an actuator to provide force feedback to a user of a force feedback device includes flowing a current through a planar coil of a flat-coil actuator included in the force feedback device, where the coil is positioned between first and second ends of a linkage. The linkage is rotated about an axis using the current and a magnetic field from at least one magnet positioned adjacent to the coil. The rotation outputs a force at the second end of the linkage, where the force is output to a user manipulandum coupled to the second end of the linkage. The rotation of the linkage is sensed with an encoder and a sensor signal is output. The sensor signal can be output to a host computer displaying a graphical environment, where images displayed in the graphical environment are updated based at least in part on the sensor signal, and where the host computer outputs a force feedback signal to the force feedback device so that the force output to the user manipulandum is based at least in part on the force feedback signal.
The apparatus of the present invention provides an integrated flat-coil actuator and mechanical linkage, which reduces the actuator size (footprint) and allows multiple versions of the flat-coil actuator to be mounted in close proximity. The embedded coil also increases the actuator heat dissipation, thereby allowing higher power output. The actuator further incorporates embedded position sensing capabilities at no significant increase in footprint size. One useful application of the inventions described herein is in the implementation of small or compact force feedback mechanisms, and is especially applicable to the low-cost mass market of force feedback devices.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawing.